Method of mining trona using a continuous miner



Nov. 19, 1963 R. F. LOVE ETAL METHOD OF MINING TRONA USING A CONTINUOUSMINER Filed May 25, 1960 2 Sheets-Sheet l GROUND LEVEL.

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METHOD OF MINING TRONA USING A CONTINUOUS MINER Filed May 25, 1960 2Sheets-Sheet 2 Th owx' m LLAK zwvwai' H15 4 OLD CAVED PANEL TRONA PILLAEIF I15 VENTORS: OBERJT F". LOVE United States Patent 3,111,306 METHOD OFMINING TRONA USING A CONTINUQUS MINER Robert F. Love, Green River, andWilliam Z. Wennehorg, Rock Springs, Wyo., assignors to FMC Corporation,a corporation of Delaware Filed May 25, 1%9, Ser. No. 31,732 6 Claims.(Cl. 2621) This invention relates to the mining of trona as found inlarge underground deposits in Sweetwater County and adjacent counties inWyoming, and in similar trona deposits found elsewhere.

The trona deposits in Sweetwater County and adjacent counties in Wyomingconsist of a main trona bed having a varying thickness up to about 16feet, averaging more nearly 7 to 13 feet, located at a depth of about1500 to 1800 feet underground.

'l his trona has a hardness index of 2.5 to 3.0, whereas soft coal has ahardness index of 1.5 to 2.0 and anthracite coal has a hardness index of2.0 to 2.5. Because of its great depth below the surface and itsrelative hardness, the main Wyoming trona bed is hard to mine and thisdifiiculty is increased by the fact that the main trona bed is strongerthan the formation above and below it.

The main trona bed lies substantially horizontal. The overlying stratais also horizontal in attitude and is chiefly composed of unconsolidatedshales and fine grained sandstones. The 400 feet of strata immediatelyabove the main trona bed is mainly weak, laminated grey shales and oilshale and an approximately 8 foot bed of somewhat plastic oil shale liesimmediately below the main trona bed. Occluded in the shales aresubstantial quantities of methane gas which is released when the shaleis broken, as when the roof of a mine caves.

The comparative strength of the trona layer and of the overlying andunderlying shale layers in average values is substantially as follows:

These conditions make conventional mining operations very difiicultbecause unlike coal and similar mining operations under a slate,compacted sandstone or other firmly compacted roof, trona miningessentially comprises removing the only strong layer in the formationand leaving an essentially Weak roof structure in the structurally weakoverlying formation while the plastic shale immediately below the tronabed is pushed upward into the mine cavity when the overlying weight isrelieved by the removal of a portion of the trona bed in the miningoperation.

In past Wyoming trona mining operation, it has been the practice to mineessentially rectangular tunnels in the trona formation according to theconventional room-andpillar mining system used in coal mining by shearcutting and drilling the trona mining face and blasting out the trona,and to leave a substantial portion of l to 4 feet of the trona adjacentthe top thereof to provide a roof support for the mine opening and tofurther support this roof section by roof bolting and timbering as incoal mining practice. This thin trona supporting roof is, however,essentially weak and because of the blasting has been further weakenedby the formation of cracks and fissures therein.

The rectangular shape of the tunnels or passages leaves the weight ofthe overburden to be supported by the thin trona layer left in place atthe roof, and provides no support for the span between the substantiallyvertical walls of the tunnels from the trona bed left in place at eachside of the tunnels, and the side Walls, weakened by the blasting, tendto buckle. Due also to the rectangular shape of the mining tunnels theoverburden weight bears at the bottom edges of the side walls, on theplastic shale layer below the trona bed and heaving and creeping of thelower shale layer into the mining cavities is aggravated thereby.

Continuous mining of the trona formation by the use of continuous miningmachines of the type illustrated, for example, in United States PatentsNos. 2,753,167, 2,836,407 and 2,872,169 is, therefore, desirable it canbe done in an economical way because the elliptical shaped tunnelsprovided by the continuous miner provide greater roof support for theuncaved tunnels, there is less heaving of the mine floor into the miningtunnels, fewer working faces are necessary and as blasting is kept to aminimum, blasting fumes and blasting cracks are reduced.

One of the objects of this invention is to provide a method of miningtrona by the use of rotary cutter boring type continuous irn'ningmachines in which the periods of idleness of the machines is materiallyreduced over the conventional mining systems.

Another object of the invention is to provide a method for continuouslymining trona by the use of continuous mining machines in which thetransport, tramming or turning of the machines from one mining face toanother is substantially reduced.

Another object of the invention is to utilize the arched or ellipticalside walls produced by rotary cutter boring type continuous miningmachines for additional roof support in the essentially weak formationin which the trona beds are found, whereby roof bolting may be reducedand smaller fenders may be left between the tunnel being mined and theadjacent mined out portion of the formation and caving of the mined outareas controlled without danger to the mining operation.

Another object of the invention is to use the arched or ellipticalcontour produced by a continuous miner in a trona mining operation andto use roof bolting only at the center of the tunnel to additionallysupport the roof at this point and to use fenders to break the cavingand prevent the caving from extending beyond a fender until such fenderis to be removed.

Another object of the invention is to cave a mined out section of themine as closely as possible to the area being mined to reduce theoverburden pressure on the area being mined.

Various other objects and advantages of the invention will appear asthis description proceeds.

Referring now to the drawings which illustrate a preferred applicationof the invention to trona mining,

FIG. 1 is a diagrammatic face view of a typical type of continuousmining machine showing the rotary cutters and of the type of tunnelwhich is cut in a trona formation.

FIG. 2 is a sectional view approximately on the line 3 2-2 of FIG. 3 oftwo mining tunnels produced by a continuous mining machine illustratingthe roof support by roof bolting and the fender left between thetunnels.

FIG. 3 is a plan view of a trona mining operation illustrating oneapplication of the method herein described.

In the operation of a continuous mining machine as illustrated in FIG. 1two rotating cutters 1 and 1a mounted on a movable frame carried bycaterpillar treads are advanced into the trona face to take circularcuts out of the trona face around axes 2 and 2a. The cuts preferablyoverlap at the midpoint of the tunnel being cut and the somewhattriangular section indicated by dotted lines a and 6a left suspendedfrom the roof 5 and projecting from the floor 6 by the operation of thecircular cutters 1 and 1a is then cut away by the horizontal sections311 and 4a of a chain cutter on the mining machine to leave anelliptically shaped tunnel substantially as illustrated in FIGS. 1 and2.

A section 5 of the trona 1 to 4 feet in thickness is preferably left atthe top of the trona bed to provide roof support for the tunnels, in theotherwise structurally weak [formation and inwardly projecting sections6b and 6c of the trona as the base of the tunnels provide greaterbearing surfaces on the underlying plastic shale layer than therectangular tunnels, provided by conventional mining methods, anddecrease heaving of the shale floor into the mining tunnels.

Due to the curved or elliptical sides 7 and 7a of this shape tunnel, thetrona roof section 5 of the mine, consisting preferably of a layer ofthe hard trona one to four feet in thickness, is better supported than arectangular mine tunnel with vertical side walls. Mine openings of thistype up to 16 feet in width, in the trona formation, can be adequatelysupported by two or three rows of roof bolts 8 having expandable anchors9 at one end and support plates 9a at the other end driven into theoverlying formation, as illustrated. In many tunnels only one row ofroof bolts through the center of the tunnel may be necessary.

We have found that tunnels up to 10 0 feet in length can be cut, withoutwithdrawing the mining machine, by merely putting in one row of roofbolts 8 spaced approximately 4 feet apart along the center line of thetunnel. Rows 8a and 8b of roof bolts may then be inserted along eachside of the tunnel after the machine has advanced far enough that theadditional rows of roof bolts may be installed without interfering withthe operation of the mining machine or the haulage of the mined tronaaway from the rear of the mining machine, if such additional roofbolting appears necessary. A lift, for example, may be driven entirelythrough a pillar up to 100 feet in thickness by installing only one rowof roof bolts down the center of the lift. A row of roof bolts may thenbe installed along each side of the tunnel approximately in the positionindicated, if this becomes desirable.

FIG. 3 illustrates the use of this type of continuous mining machine inthe extraction of pillars in a trona mine. In this figure parallelentries :10, 10a, 10b, 10c, 10d and 10a are illustrated as having beendriven into the trona formation from primary development entries (notshown) at the right side of this figure. Entry 10c may be an uncavedentry of a previous secondary entry development panel to the north ofthe mining area shown in FIG. 3. Entries 10, 10a, 10b and 10a may bepart of the entries of new secondary development panel which when firstdriven extended further into the now caved formation to the left, asindicated by the dotted line extension of entries 10 and 10a, 10171 and10c. Entry 10b is shown as provided with a belt conveyor 11'on which thetrona removed from the formation is deposited for removal from the mine.Entries 10 and 10c are used for the main inlet and outlet of ventilatingair as indicated.

At right angles to the entries 10, 10a, 10b, 10c and 10d, rooms 11a,11b, 11c, 116L119, 1 1 etc., have been driven to divide the trona areato be extracted into tiers of substantially rectangular pillars 12. Theoutlines of two former rooms lie and 11], which are now in the cavedarea of the mine, are indicated in dotted lines. Originally the entries10, 10a, 19b, etc., and the rooms 11e, 117, etc., extended further tothe left of FIG. 3, but as the trona pillars 12 were mined, on retreatfrom the furthest extension of this development, the roof over the minedout area was caved to relieve pressure on the formation and these formerentries and rooms are now lost in the caved area to the left of FIG. 3.

The exact number and arrangement of the entries and rooms is notmaterial to the invention herein described as long as the number andarrangement is sufficient to provide access to the formation for thepurpose of mining and removal of the trona and as long as thearrangement is sufiicient to provide two or more pillars through whichthe continuous mining machine can be driven substantially withoutturning to drive lifts through two or more pillars for the purpose ofremoving the pillars.

The use of a continuous miner in this operation is shown on the stillexistent pillars 12a, 12b, 12c, 12d and =12e, at the left of FIG. 3. Ashere illustrated a rotary cutter continuous miner 13 of the typeillustrated in FIG. 1 and more completely illustrated and described, forexample, in United States Patents Nos. 2,753,167, 2,836,407 and2,872,169, has been star-ted from the entry 10 and has driven lifts 14,14a, 14b through pillars 12a, 12b and 120 and lift 14c partial throughpillar 12d in the tier of pillars at the left of FIG. 3. The directionand sequence of mining the future lifts is indicated by the letters a,b, c, d, e, f, g, h, i, j, k, l, in pillars 12a to 12.

In this operation the miner 13, which is a heavy piece of equipment,difficult to move and turn in the cramped quarters of the mine operatescontinuously in one direction (from south to north) to drive liftsthrough the tier of pillars 12a, 12b, 12c, 12d and 12e, is turned aroundin entry 102 and drives lifts c, d, e, f, and g ,(from north to south)through the tier of pillars 1 2e, 12d, 12c, 12b and 12a where it isagain turned around to start mining lifts h, i, j, k, and l in theopposite direction. This operation is continued until all of the tier ofpillars 12a, 12b,

12c, 12d and 12s have been extracted, after which mining the nextadjacent tier of pillars 1 2 to the right is started.

Between each lift 14, 14a, 14b, 14c, etc., and the next adjacent room orlift to the left of FIG. 3 a narrow fender of trona 15, 15a, 15b, 15c,etc., approximately three feet wide at its narrowest portion, is left inthe mining operation and as soon as the lift is driven through the nextpillar 12 this fender is removed, by drilling and blasting, to permitthe roof of the mined out section of the pillars to cave and relieve thepressure. As indicated on the drawings, the fender 15 formerly leftbetween the lift 14 and the previously caved area has been blasted andthe roof caved and the fender 15a is being readied to blast. As soon asthe miner 13 has passed entirely through lift a in pillar 12d, fender15b in pillar may be blasted and the roof caved. In this way caving ofthe mined out area, to relieve pressure in the active mining area,proceeds as the mining operation proceeds.

As only one working face is required, by the use of a continuous miner,and as the caving in the rear of the miner is planned and can becontrolled, no unexpected release of gas into the mine is encounteredand the amount of ventilating air required in each active working areacan be reduced approximately 40% below that required for the same mineoutput in the older process of drilling and blasting out the trona.

By the arrangement of entries 10, 10a, 10b, 10c, etc., as illustrated,during the driving of any lift the mined trona can be hauled from therear of the miner 13 to the nearest entry and from this entry to theconveyor 11, and when 'a given lift is finished and a lift started inthe next adjacent pillar, a new haulageway is opened up in the entryjust crossed by the miner so that the portion of the lift to beabandoned and caved may be caved by drilling and blasting the fenderwithout interfering with the haulage from the miner 13.

For example, during the driving of lift 14b in pillar 120 the haultage,normally by shuttle car, will be along passage 17a in the entry b to theconveyor 11. When lift 14b is finished and lift 14c started, a newhaulage- Way is available and the haulage will be through haulageways17b and 17c to conveyor 11. Haulageway 17a will no longer be needed andcaving of lift 14a can proceed, without fear that the caving will blockhaulageway 17b. Likewise when lift 14c is finished and the lift b inpillar 12e started, another new haulageway in entry 10d is opened sothat blasting of the fender b and caving of the roof of lift 14b can bestarted. It is preferable to leave the fender adjacent the justcompleted lift in place until the next lift has been completed so thatthere is at least one unblasted fender behind the lift being driven.This plan of mining can be followed regard-less of whether the miner isproceeding from bottom to top (south to north) or top to bottom of themining plan illustrated in FIG. 3.

In the mining plan described, the miner 13 can proceed substantially ina straight line to drive lifts through pillars 12a, 12b, 12c, 12d, 12a,etc., and then with one turn in the end entry to drive lifts c, d, e, fand g in the opposite direction, through these pillars until this seriesof pillars is extracted. Roof bolting to the extent necessary canproceed behind the miner 13 without withdrawing or idling the minerduring the roof bolting. The fenders 15, 15a, 1517, etc. can be drilledand blasted to cave the roof of the mined sections as soon as the nextsucceeding lift is finished, and by the arrangement of rooms or crossentries 17, 18, 19 and 20 haulageways are always available as each newlift is started, Blasting of the fender on the outside of a lift doesnot cause shattering or blasting cracks in the roof toward the inside ofthe lift.

In the cross section of FIG. 2, the lift 14b is indicated and, in dottedlines, the outline of the next adjacent lift (or room) to the left hasbeen shown. The fender to the left of this lift (or room) has beenblasted and the roof caved as indicated by the arrows prior to thedriving of lift 14b. Due, however, to the arched contour of the top offender 15b formed in driving the previous lift to the left of fender15b, the roof caving has broken along the line 21 so that the cavingdoes not extend into the arched top of fender 15b, which at the time ofthe previous caving was an arch from a solid pillar, and the roof oflift 142; when driven remains substantially intact until fender 15b isblasted out. Blasting cracks do not extend substantially outside thefender being blasted. If desired, the roof bolts 8 may be withdrawnbefore a lift is caved.

While a representative section of a mine has been shown, for purpose ofillustration, in FIG. 3, it will be understood that a greater or lessernumber of longitudinal entries may be in use at the same time and thatthe transverse entries will vary in number from the mining face mostremote from the main development entries, to the mining area closest tothe main development entries as the mining and caving progresses, onretreat, from the remote to the nearest transverse entry. It will alsobe understood that various modifications and changes can be made in themining plan described, without departing from the spirit of thisinvention or the scope of the following claims.

We claim:

1. The method of mining trona by the use of a continuous miner, whichcomprises driving a series of substantially parallel entries into thetrona bed, driving a series of substantially parallel rooms at angles tothe entries to divide the area to be mined into tiers of pillars anddriving lifts in a substantially straight line through a tier ofpillars, turning the mining machine and driving lifts in a substantiallystraight line in the opposite direction through said tier of pillarsuntil each successive tier of pillars is extracted leaving a narrowfender of trona between each lift and the previously mined area and whena lift through the next pillar of a series of pillars has beencompleted, caving the fender and the roof of said previously mined lift.

2. The method of mining trona by the use of a continuous miner, whichcomprises driving a series of substantially parallel entries into thetrona bed, driving a series of substantially parallel rooms atsubstantially right angles to the entries to divide the area to be minedinto tiers of substantially rectangular pillars and driving lifts in asubstantially straight line through a tier of pillars, turning themining machine and driving lifts in a substantially straight line in theopposite direction through said tier of pillars until each successivetier of pillars is extracted leaving a narrow fender of trona betweeneach lift and the previously mined area and when a lift through the nextpillar of the tier has been completed, caving the fender and the roof ofthe previously mined lift.

3. The method of mining trona by the use of a continuous miner, whichcomprises driving a series of substantially parallel entries into thetrona bed, driving a series of substantially parallel rooms atsubstantially right angles to the entries to divide the area to be minedinto tiers of substantially rectangular pillars and driving lifts in asubstantially straight line through a tier of pillars, turning themining machine and driving lifts in a substantially straight line in theopposite direction through said tier of pillars until each successivetier of pillars is extracted leaving a narrow fender of trona betweeneach lift and the previously mined area and when a lift through the nextpillar of the tier has been completed, caving the fender of thepreviously mined lift and caving the roof of said previously mined lift,and using the entry at the rear of each lift in the direction of miningas a haulageway for the mined trona.

4. The method of mining trona by the use of a continuous miner, whichcomprises driving a series of entries into the trona bed, driving aseries of rooms at angles to the entries to divide the area to be minedinto a plurality of pillars and driving lifts in a substantiallystraight line through a plurality of pillars, turning the mining machineand driving lifts in a substantially straight line in the oppositedirection through the same plurality of pillars until each successivegroup of pillars is extracted leaving a narrow fender of trona betweeneach lift and the previously mined area and when a lift through the nextpillar of a series of pillars has been completed, caving the fender andthe roof of the previously mined lift.

5. The method of mining trona by the use of a continuous miner, whichcomprises driving a series of substantially parallel entries into thetrona bed, driving a series of substantially parallel rooms atsubstantially right angles to the entries to divide the area to be minedinto substantially rectangular pillars, driving elliptically shapedlifts through the pillars to remove the pillars while leaving narrowfenders between each lift and the previously mined area, leaving aportion of the trona in place at the top of each lift to provide asupporting roof, installing a row of roof bolts through the center ofthe lift roof as the driving of the lift progresses, turning the miningmachine and driving lifts in a substantially straight line in theopposite direction through the said pillars until each successive groupof pillars is extracted and caving the fender and roof of the previouslymined lift adjacent to the mined out area after the next lift iscompleted.

6. The method of mining trona by the use of continuous miner, whichcomprises driving a series of substantially parallel entries into thetrona bed, driving a series of substantially parallel rooms atsubstantially right angles to the entries to divide the area to be minedinto substantially rectangular pillars, driving elliptically shapedlifts with narrow fenders th ough the pillars to remove the pillars,leaving a portion of the trona in place at the top of each lift toprovide a supporting roof, installing a row of roof bolts through thecenter of the lift roof as the driving of the lift progresses,installing a row of roof bolts on approximately four foot centers alongthe roof at each side of the elliptical shaped lift at substantially thepoint where the sides of the ellipse begin to curve downwardly, turningthe mining machine and driving lifts in a substantially straight line inthe opposite direction through the said pillars until each successivegroup of pillars is extracted and Where a lift has been completed cavingthe fender and the roof of the completed lift after the next lift iscompleted.

References Cited in the file of this patent UNITED STATES PATENTS2,753,167 Brown July 3, 1956 2,778,622 Reis Jan. 22, 1957 2,859,682 JoyNov. 11, 1958 OTHER REFERENCES Mechanical Loading of Coal Underground,Author, Given, first edition, copyright 1943, pages 342 and 343 reliedon.

Mining Congress Journal, vol. 38, Issue 8, pages l05107, August 1952.

Mining Congress Journal, July 1953, pages 44 and 45.

1. THE METHOD OF MINING TRONA BY THE USE OF A CONTINUOUS MINER, WHICHCOMPRISES DRIVING A SERIES OF SUBSTANTIALLY PARALLEL ENTRIES INTO THETRONA BED, DRIVING A SERIES OF SUBSTANTIALLY PARALLEL ROOMS AT ANGLES TOTHE ENTRIES TO DIVIDE THE AREA TO BE MINED INTO TIERS OF PILLARS ANDDRIVING LIFTS IN A SUBSTANTIALLY STRAIGHT LINE THROUGH A TIER OFPILLARS, TURNING THE MINING MACHINE AND DRIVING LIFTS IN A SUBSTANTIALLYSTRAIGHT LINE IN THE OPPOSITE DIRECTION THROUGH SAID TIER OF PILLARSUNTIL EACH SUCCESSIVE TIER OF PILLARS IS EXTRACTED LEAVING A NARROWFENDER OF TRONA BETWEEN EACH LIFT AND THE PREVIOUSLY MINED AREA AND WHENA LIFT THROUGH THE NEXT PILLAR OF A SERIES OF PILLARS HAS BEENCOMPLETED, CAVING THE FENDER AND THE ROOF OF SAID PREVIOUSLY MINED LIFT.